从数组中对象取出单一或多个属性创建新数组

const createArrFromObj = (arr, keys) => {
    let newArr = []
    if(typeof(keys) == 'string') {
      newArr = arr.map(item => item[keys])
    }else if(Array.isArray(keys)) {
      let len = keys.length
      newArr = arr.map(item => {
        let i = -1;
        let item_ = {}
        while(++i < len) {
          // console.log(item, keys[i]);
          item_[keys[i]] = item[keys[i]]
        }
        return item_
      });
    }
    return newArr
  }
  // example
  var arr = [{a: 1, b: 2, c: 3}, {a: 4, b: 5, c: 6}]
  createArrFromObj(arr, ['a', 'b']) // [{a: 1, b: 2}, {a: 4, b: 5}]